Clear Sunscreen: How Light Interacts with Matter
Version 4. Last updated: May 1, 2008.

This unit explores issues related to size and scale, specifically the effect of
the size of nanopowders on the interactions of energy and matter (e.g., the absorption
of light, addressing the electromagnetic spectrum and associated wavelengths).
For example, old sunscreens use "large" zinc oxide particles, which block ultraviolet
light but scatter visible light, giving the cream a white color. If nanopowders of
zinc oxide are used instead, the cream is transparent, because the diameter of each
nanoparticle is smaller than the wavelength of visible light.

Upon completing this unit, students will understand:

How the energies of different wavelengths of light interact differently
with different kinds of matter.

Why particle size can affect the optical properties of a material.

That there may be health issues for nanosized particles that are undetermined at this time.

That it is possible to engineer useful materials with an incomplete understanding of their properties.

There are often multiple valid theoretical explanations for experimental data; to find out
which one works best, additional experiments are required.

How to apply their scientific knowledge to be an informed consumer of chemical products.

Length: 5 lessons, up to 11 50-minute classroom periods if all lessons are used. Not all lessons are required.
Use the lessons most appropriate for your students. A one-day version is also available.

Download a zip archive of the Microsoft
Word and PPT source files (35 MB) if you want to adapt the materials
under the Creative Commons license. PowerPoint [PPT] versions of the slides
are also available separately, below.

If you would like to have a copy of the animation on your computer for offline viewing,
download the following files to the same folder, and then open the sunscreenanimation.html file
in your web browser.